The present invention relates generally to tubular fabric formed on small diameter circular knitting machines and, more particularly, to an apparatus and knitting machine that produces large rolls of such material.
Small diameter circular knitting machines have been in use for many years in the textile industry. These machines are especially designed for knitting narrow tubular single jersey and rib knit polyester and cotton fabrics, and combinations thereof, to be used as cuffs on sleeves or trousers, as liners for specialty garments, etc.
While there are several types and models of small diameter circular knitting machines, they each operate on the same general principles. A small diameter knitting cylinder and dial assembly equipped with latch needles (knitting needles) receives ends of polyester or other yarn that are fed from surrounding creels. A small diameter tubular knitted fabric is thus formed on the latch needles and is continuously and synchronously drawn downward by the machine""s takedown assembly. The takedown assembly includes two or more takedown rollers that frictionally engage and pull downward on the tubular fabric. As is conventional in machines of this type, a windup mandrel is positioned below the takedown rollers to form a narrow roll (like a coiled fire hose) of fabric having a width corresponding to the width of the tubular, but flattened, knitted fabric. The roll is wound around the mandrel, the mandrel being independently driven and controlled by a clutch assembly.
There are a number of problems inherent in this system of forming rolls of fabric. First, because these rolls are formed by a buildup of concentric layers, the rolls are limited in the diameter that can be formed. Thus the length of fabric on a roll must also be limited. As a result, these narrow rolls of fabric must be xe2x80x9cdoffedxe2x80x9d, or removed, about every 35 to 40 minutes, depending upon the production rate of the machine. This translates to a substantial labor requirement wherein machine operators must frequently remove the full rolls and ready the machine for a new roll. Similarly, the end users of the narrow fabric rolls are forced to frequently interrupt the production of apparel or the like in which the tubular fabric is being incorporated in order to get a new roll.
In such machines, typically the mandrel, or core, of the narrow roll is driven independently by a clutch-controlled motion. As a result, the tension created in the fabric is not uniform throughout the roll. A great deal more tension tends to be induced on the inner, or first, layers than on the outer layers because the mandrel exerts a greater force on the inner layers and less force on the outer layers. This is caused by decreasing the angular velocity of the outer layers as the clutch tends to brake. Fabric, like any other material having a substantial elastic characteristic, develops a memory when held in a certain stretched or unstretched condition for any appreciable length of time. The problem that this creates is that the end users must produce apparel with a product that does not exhibit uniform characteristics throughout its length. For example, if the tubular fabric is being cut into specified lengths for use as cuffs on garments, the first cuffs, which are stretched less, will be more loosely fitting because the less stretched fabric will have less tendency to return to a narrow, stretched shape. On the other hand, the last cuffs formed will fit more tightly as the material that is stretched during the fabric formation tends to return to its narrow, stretched shape. This presents a quality dilemma for the end user who often must discard lengths of the knitted fabric as unusable.
Yet another problem inherent in the production of narrow rolls is wastage resulting from knitting machine failures such as sudden stoppage, which causes the very narrow rolls to collapse and unravel, rendering them useless.
The present invention is directed to an apparatus and method that addresses each of the problems described above.
The essence of the present invention is a takeup system that forms a larger, wider, roll of tubular knitted fabric and also maintains a constant tension on the fabric wound onto the takeup package. In its simplest form, the system includes a traversing mechanism that is positioned between the knitting cylinder and the takedown rollers. The traversing mechanism moves at a controlled rate across the path of the fabric tube to build a wound package of a substantially constant diameter. Secondly, the takeup package is surface driven to ensure a constant tension on the fabric on the package.
The traversing mechanism is mounted between the knitting cylinder and the takedown rollers and includes a traversing control spindle that extends substantially across the width of the machine""s takedown assembly. The traversing control spindle is mounted by flange bearings at each end attached to the upper takedown bracket. A reversing nut is operatively mounted on the traversing control spindle and reciprocates along tracks in the traversing control spindle. Upon reaching the end of the track, the nut reverses direction and moves back to the opposite end, and so on. If the tracks were provided with a conventional, constant pitch, the reciprocating motion would be accelerated near the ends of the spindle. Therefore, an important aspect of the spindle track pattern in the present invention is that the pitch of the track pattern is steeper at the ends of the track and is more gradual in the middle of the track. This unique design causes the reversing nut to move more slowly when it approaches the ends of the track than it does at the middle of the spindle, which actually causes a more constant traversing speed. As a result, the fabric being pulled downwardly is more evenly wound across the width of the fabric roll.
A traversing plate is fastened to one end of the reversing nut so that, as the traversing control spindle rotates, the traversing plate moves with the reversing nut back and forth along the spindle. A guide rod extends through a slot in the traversing plate and is attached on opposite ends to the flange bearings. The guide rod keeps the traversing plate in a constant horizontal and vertical alignment with respect to the takedown rollers. Extending outwardly from the bottom of the traversing plate is a narrow, flat guide plate that is slightly wider than the width of the tubular fabric being processed. Small rollers having rotational axes perpendicular to the takedown rollers are attached on opposite sides of the guide plate and protrude forwardly outward so that they contact the vertical side edges of the tubular fabric. To stabilizethe fabric, a separate fabric spreader plate is inserted within the tubular fabric sleeve to spread and stabilize the fabric being pulled through by the takedown rollers. Thus, as the spindle rotates, the reversing nut with attached traversing plate moves back and forth along the length of the spindle. The guide plate, with rollers, moves the fabric with the spreader plate in similar fashion back and forth substantially along the length of the takedown rollers as the fabric is pulled through the takedown rollers.
A second aspect of the invention is to provide constant tension on the rolled fabric. Toward this end, the takeup mandrel and clutch assembly of the conventional machine are removed and replaced by a freely rotating takeup roller that extends across a substantial width of the lower takedown bracket. Opposite ends of the takedown roller shaft are held by spring-biased arms that are each mounted on opposing walls of the lower takedown bracket.
The independent drive system of the conventional machine is removed from the machine of the present invention and is replaced by a knurled, cylindrical surface driving windup roller that extends across the width of the lower takedown bracket. Opposite ends of the windup roller shaft are mounted within pillow block bearings. The windup roller is interconnected with the takedown rollers by a gear chain and driven in a ratioed relationship thereto. Thus, as the takedown rollers pull the fabric downward for winding upon the takeup roller, the windup roller is driven slightly slower, relaxing some of the tension in the fabric. The biasing arms holding the takeup roller and thus the fabric roll against the windup roller. The windup roller then drives the fabric roll from the roll""s outer surface at a constant speed. This constant surface speed ensures that a constant tension is induced on the knitted fabric as it is being wound around the takeup roller. Therefore, a fabric roll is formed that has a substantially uniform outer shape, holds 5 to 10 times more fabric than a conventional, narrow roll, and delivers a fabric wound at a substantially uniform tension.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.